Frequency divider



S. W. SEELEY FREQUENCY DIVIDER Filed Feb. 14, 1947 Jan. 16, 1951 SW.@25V -kr. @my

` Patented Jan. 16, 1951v 2,538,277 FREQUENCY DIVIDER Stuart WilliamSeeley, Roslyn Heights, N. Y., assgnor to Radio Corporation of America,a corporation of Delaware' Application February 14, 1947, Serial No.728,394

(Cl. Z50-36) 11 Claims.

and more particularly to a simplified and improved frequency divider.

An object of the invention is to provide a stable frequency divideremploying a single tube and a delay line in circuit therewith, andcapable of dividing by two, four, six, etc., depending upon theconstants of the delay line.

` Another object of` the invention is to provide a frequency dividerwhich can be keyed to start or stop within a fractional period of acycle of the,i frequency to be divided, and which provides uniformoutput impulses during the entire keying ON interval without variationof either amplitude or phase of these impulses during the i ON interval.

Another object of the invention is to provide a stable frequency dividerwhich may be keyed without the introduction of transients.

Another object of the present invention is to provide a frequencydivider which can be keyed and satisfies the requirements (l) of anegligible leakage of the input energy to the output terminals, (2)provides output impulses whose Wave forms are substantial replicas ofthose portions of the input wave forms which have a given polarity, and(3) provides (during a keying interval) a predetermined number ofuniformly spaced impulses whose wave forms and peak amplitudes areidentical.

Although many types of frequency dividers are known in the art, suchdividers suffer from numerous disadvantages; and none of them, havingthe simplicity of the frequencyvdivider of the present invention, fulllall of the objects stated above.

Amore detailed description of the present invention follows inconjunction with the drawings, wherein:

Fig. 1 illustrates a simpliiied form of frequency divider embodying theprinciples of the present invention;

Figs. 2a., 2b and 2c are graphs given in explanation of the operation ofthe frequency divider of the invention; and

Fig. 3 illustrates a preferred form of frequency divider of thisinvention.

The same or equivalent parts of the embodiments of Figs. 1 and 3 arelabeled by the same reference characters.

Referring to Fig. 1, there is shown a frequency divider comprising atriode vacuum tube I whose anode is connected through the secondarywinding of a transformer TR. to one end of an articial line TL. Theother end of the line TL is connected through a' lead I2 to the grid ofthe tube. Line TL is a constant K lter which is composed of amultiplicity of series inductances and shunt capacitances. That end ofline TL which is connected to the grid is terminated by a resistor I3whose Value is equal to the surge impedance of the filter. One side ofthe line TL is connected to ground. The cathode of the tube IIl is alsogrounded. The primary winding of the transformer TR is connected to thesource of energy whose frequency is to be divided. The output terminals,from which spaced impulses are obtained, are designated I4.

The operation of Fig. 1 may be better understood by reference to thegraphs of Figs. 2a., 2b and 2c. Let it be assumed, for example, that theenergy of the driving source is a sine wave of 360 kilocycles. Fig. 2agraphically shows such a sine wave, whose value is zero at times A', A,B, C, D, E, F etc. The positive half cycles of the sine wave of Fig. 2acause current to flow through the 'tube I Il in the absence of anegative grid voltage. However, when the tube conducts on a firstpositive half cycle, a voltage drop (equal to the surge impedance of thefilter TL multiplied by the anode current flowing through the tube) isimpressed on the input of the filter TL. This voltage drop constitutesan impulse which is shown in Fig.4 2b between times A and B, and thisimpulse travels down the line TL toward the resistor I3, arriving at theterminating resistor I3 between the times C and D as shown in Fig. 2c.This impulse in Fig. 2c is of negative polarity with respect to groundand is impressed upon the grid of the tube l0 by way of conductor I2.The time constants of the line TL are so chosen that the negativeimpulseimpressed on the grid occurs during the time when the immediatelysucceeding positive half cycle of Fig. 2 is impressed on the anode ofthe tube. This negative impulse which isapplied to the grid of tube I0is of such magnitude as to prevent the tube Ill from drawing currentduring its occurrence.. It will thus be seen from an inspection of thegraphical representation of Figs. 2a, 2b and 2c that the tube Ill drawscurrent only during alternate positive half cycles of the applied inputwave.

Although the system of Fig. 1 has been described with particularreference to a frequency halver, it will be obvious that the constantsof the filter TL may be selected so as to delay the negative pulsesapplied to the grid by periods of two. three or any integral number ofcomplete cycles of the input wave. For instance, if the delay time ofthe filter TL is equal to two cycles of the input wave, both the rst andsecond positive portions of that wave will cause current to ow in thevacuum tube I0, and a pair of negative pulses corresponding to thoseanode current pulses will be applied to the input of the filter TL. Thispair of pulses being subjected to the two cycle delay time of the newfilter TL, will now be impressed on the grid during the third and fourthpositive half cycles of the input wave and prevent the passage of anodecurrent at those particular times. Thus, anode current will ow for twohalf cycles, be cut 01T for two half cycles, again flow for two halfcycles, etc. In this manner the output energy will have a componentwhose frequency is one-quarter of that of the input wave. In the samemanner, if the filter were designed to have a delay time equal to threecycles of the `input wave, the output of the device would consist ofgroups of three pulses followed by a quiescent period equal to threecycles, etc., thus giving an Output component at one-sixth of thefrequency of the input wave.

Fig. 1 has been illustrated and described in order to explain the broadprinciples of the invention. However, for certain applications, thesystem of Fig. 1 may require additional features to overcome leakage ofthe input energy to the output terminals.

The system of Fig. 3 is a preferred embodiment of the invention and isdesigned to minimize leakage of the input wave to the output terminalsI4. Referring to Fig. 3 in more detail, there is shown a pentode vacuumtube 20 whose anode is 'connected via lead 2I to terminal TI of thesecbndary 22 of the transformer TR. Terminal T2 of transformer TR isconnected via lead 23 to the input end of an artificial line or constantK filter TL. The output end of the line TL is terminated by a resistorI3 whose value is equal to the surge impedance of the line TL, and isalso connected via lead I2 to the first grid of the vacuum tube 20. Theinput wave whose frequency is to be divided is applied to the primaryYwinding of the transformer TR. Y

If the screen grid SG of vacuum tube 20 is supplied with positivevoltage and the suppressor grid SP is connected to the cathode (asshown), the portion of the circuit of Fig. 3 so far described wouldoperate exactly as explained in connection with Fig. 1. However, if thedevice is to divide frequenciees of the order of a few hundredkilocycles or higher, the normal capacitive leakage between the terminalTI of the secondary 22 and ground may cause current at the appliedfrequency to flow through the filter TL regardless of whether or nottube 20 is conducting, and thus impress an undesirable amount of theapplied frequencyY between the output terminals I4. To overcome thisdiiiiculty, secondary 22 of transformer TR' has been extended to a thirdterminal T3 in order to produce a potential opposite to that applied tothe anode, and a balancing condenser 25 is connected between terminal T3and ground in order to allowfor neutralization of the capacity currentsin accordance with wellknown principles. In case there should also beconductive leakages of the input energy to ground, these may also beneutralized by the inclusion of a resistor of the proper size fromeither terminal TI to ground, or from T3 to ground, as the case mayrequire. Resistor R is one such resistor and can be eliminated in manycases. If desired, the entire secondary of transformer TR may beresonated to the input frequency by means of a condenser 26 shuntedbetween terminals TI and T3. This procedure, however, is only applicablein the case wherein the input frequency is a sine wave.

The system of Fig. 3 lends itself to keying, and this may beaccomplished by applying a square wave keying pulse of positive polarityto the screen grid SG. The occurrence 'time and repetition rate of thissquare wave keying pulse should be synchronously related to thefrequency of the drive source, so that the starting edge of the keyingpulse occurs during the time interval when the anode of the tube 26 isnegative with respect to the cathode. In this way, the frequency dividerof the invention will be ready to operate on the succeeding positivehalf cycle of the input wave. The keying wave may, if desired, have aduration equal to ten or more complete cycles of the l'input waveenergy, and all of the output pulses during that interval will occur ata submultiple rate with respect to the input frequency and will beuniformly spaced and have the same peak amplitude and the same waveform.

It should be noted that the anodes of the tubes of Figs. 1 and 3 havenot been provided with a positive polarizing B+ potential such as iscustomarily provided in conventional circuits. This anode polarizingpotential is not necessary in this case because the driver voltage hassufcient magnitude to cause anode current to ow dur-ing the desiredintervals. It should be distinctly understood, however, that theinvention is not limited to this specific arrangement since, if de-ysired, an anode 'polarizing potential may be sup'- plied. Although theterminating resistor I3 has been shown connected to the output end ofthe artificial line it should be understood that, if desired, thisresistor may be connected to the input end of the line, or the line maybe terminated on both ends by resistors. Another alternative stillwithin the scope of this invention is to construct the artificial lineof elements with sufficient dissipation so that no termination isnecessary.

The invention is not limited to the specific embodiments described andYillustrated. For instance, other means for ,keying the device of theinvention may employ the cathode impedance of a vacuum tube shuntedacross the input to the transmission line TL to prevent the initiationof voltage pulses in that line in the labsence of a keying wave ofnegative polarity applied to a control element of the vacuum tube usedto supply this cathode shunting impedance.

What is claimed is:

1. A frequency divider comprising a vacuum tube `having an anode, and agrid, a delay line having one terminal connected tosaid anode andanother terminal connected to said grid, a source of energy .whosefrequency is to be divided icou; pled to the anode of saidl tube in suchmanner as to supply suflicient polarizing potential to cause saidtube todraw current ,during predetermined portions of the input wave, tothereby cause 'a voltage wave to travel along lsaid line from theterminal connected to said anode, saiddelay'line having such constantsbetween said terminals and being so constructed and arranged that thevoltage wave traveling thereover when said tube draws current is delayeda predetermined intel gral number of cycles of theinput waveV beforebeing applied to said grid in such sense and mag; nitude as to preventsaid tubev from drawing current during the interval the delayed voltagewave is applied toi said'v grid; said frequency constant K filter linehaving one end connected to said anode and its other end connected tosaid grid, a connectionfrom said cathode to one side" of said line, aterminating resistor connected to.

said line, means including a driver source for supplying the frequencyto be divided to lthe anode of said tube through a transformer, saidfrequency divider being so constructed and arranged that there is anabsence of anode current flow therein in the absence of applied wavesfrom said driver, said applied waves having such magnitude as to causesaid tube to draw current at certain predetermined intervals, to therebyproduce a voltage pulse whenever said tube draws current and whichtravels along said line from the anode end to the grid end, said filterline having such constants that it produces a delay in the voltage pulsetraveling along its length which islequal to a predetermined integralnumber of cycles of the applied wave.

'3. A frequency divider comprising a pentode vacuum tube having ananode, a cathode, and a plurality of grids, an articial line having onee'nd connected to said anode and its other end Y connected to a grid, aconnection from said cathode to'said artificial line, means forsupp-lying fundamental frequency waves to said anode through atransformer, said frequency divider being so constructed and arrangedthat said tube des not draw current in the absence of applied Waves fromsaid means, said tube producing'a voltage pulse whenever it draws anodecurrent and which pulse travels along said line, said line having suchconstants that it produces a delay in the voltage pulse traveling alongits length which delay is equal to a predetermined integral number ofcycles of the fundamental frequency wave, and a source of keying wavescoupled to another grid of said tube, the repetition rate of said keyingwaves being synchronously related to the waves of said fundamentalfrequency and so phased that'the starting edge of the keying wave occursduring the time interval that said tube is not drawing current.

"4. A frequency divider comprising a Vacuum tube having an anode, acathode, and a grid,'a delay line having one terminal connected to saidanode and another terminal connected to said grid, a source ofsinusoidalV wave energy whose frequency is to be divided coupled to saidanode of said tube in such manner as to cause said tube to draw currentduring predetermined portions of the input wave to thereby cause avoltage wave to travel along said line from the terminal connected tosaid anode, said delay line having such constants between said terminalsthat the voltage wave traveling thereover when said tube draws currentis delayed a predetermined integral number of cycles of the input wavebefore being applied to said grid in such sense and magnitude as toprevent said tube from drawing cur.- rent during the interval thedelayed voltage wave is applied to said grid, and means for keying saidtube by supplying to said frequency divider a keying wave ofpredetermined polarity at intervals which are synchronously related tothe frequency of the input wave and so phased that the positive risingedge of the keying wave occurs during the time interval that said anodeis negarI tive with respect to the cathode.

5. A frequency divider comprising a vacuum tube having an anode, a,cathode and a grid, a delay line having one end connected through a coilto said anode and its other end connected to said grid, a connectionfrom said cathode to one side of said line, means for supplying to Lsaidcoil the frequency to be divided to enable said tube to draw currentduring predetermined portions of the input wave, to thereby cause avoltage wave to travel along said line from the terminal connected tosaid anode, said delay line having such constants between said terminalsthat the voltage wave traveling thereover when said tube draws currentis delayed a predetermined integral num-v ber of cycles of the inputwave before being applied to said grid in such sense and magnitude as toprevent said tube from drawing current during the interval the delayedvoltage wave is applied to said grid.

6. A frequency divider comprising a vacuum tube having an anode, acathode and a grid, a delay line having one end connected through a coilto said anode and its other end connected to said grid, a connectionfrom said cathode to one side of said line, a connection from saidcathode to ground, means for supplying to said 'coil the frequency to bedivided, an inductive extension for said coil, and a 'balancingcondenser connected between ground and that terminal of said extensionwhich is furthest removed from 'said coil, means for preventing saidtube from drawing current in the absence of energy from said source,said tube producing a voltage wave whenever it draws current whichtravels along said line in a direction away from the anode terminal ofsaid line, said delay line having such constants between said terminalsthat the voltage wave traveling thereover when said tube draws currentis delayed a predetermined integral number of cycles of the input wavebefore being applied -to said grid in such sense and magnitude as toprevent said tube from drawing current during the interval the delayedvoltage wave is applied to said grid.

'7. A frequency divider comprising a vacuum tube having an anode, acathode and a grid, a delay line having one end connected through a coilto said anode and its other end connected to said grid, a connectionfrom said cathode to one sideof said line, a connection from saidcathode to ground, a means for supplying to said coil the frequency tobe divided, an inductive extension for said coil, and a balancingcondenser connected between ground and that terminal of said extensionwhich is furthest removed from said coil, a condenser across said coiland extension for tuning the same to the frequency of said source, meansfor preventing said tube from drawing current in the absence of energyfrom said source, said tube producing a voltage wave whenever it drawscurrent which travels along said line in a direction away from the anodeterminal of said line, said delay line having such constants betweensaid terminals that the voltage wave traveling thereover when said tubedraws current is delayed a predetermined integral number of cycles ofthe input wave before being applied to said grid in such sense andmagnitude as to prevent said tube from drawing current during theinterval the delayed voltage wave is applied to said grid.

8. A frequency divider comprising a vacuum tube having an anode, acathode and a grid, a

delayv line yhaving one end' connected through a coil to said anodetandits other end connected to saidigrid, a connection from said cathode toone side -of said line, a connection from said cathode to ground, aterminating dissipative resistor coupled to said delay line, a source'ofenergy whose frequency is to be divided coupled to said coil,

` an .inductive extension for said coil, and a balancing condenserconnected between ground and that terminal of said extension which isfurthest removed from said coil, a condenser across said coil andextension for tuning the same to the frequency of said source, means forpreventing said tube from drawing current in the absence of energy fromsaid'source, said tube producing a voltage wave whenever it drawscurrent which travels along said line in a direction away from the anodeline terminal, said delay line having such constants between saidterminals that `the voltage wave traveling thereover, when said tubedraws current is delayed a predetermined integral number of cycles ofthe input wave before being applied to said grid in such sense andmagnitude as to prevent said tubeY from drawing current during theinterval the delayed voltage wave is applied 'to said grid, said meansincluding a source of keying pulses whose repetition rate is lower thanand synchronously related to the frequency of said source of energy.

9. In a Vacuum tube frequency divider containing a control electrode,the method of dividing the frequency of an input wave which comprisescausing said tube to conduct current at certain predetermined intervalsof the input wave, producing a voltage pulse whenever said tube drawscurrent, delaying this voltage pulse a predetermined integral number ofcycles of the input wave, applying said delayed voltage pulse to acontrol electrode of the vacuum tube in such sense and magnitude as toprevent said tube from drawing current during the time said delayedvoltage pulse is applied to said control electrode, and applying keyingwaves to said vacuum tube at times synchronously related to thefrequency of said input waves but `such that the start of the keyingwave occurs during the time interval that said tube does not drawcurrent.

v 10. A `frequency divider comprising a vacuum tube having an anode, acathode and a grid, a

lter line having one end connected to said anode f and its other endconnected to said grid, a connection from said cathode to one side ofsaid line, a terminating resistor connected to said line, meanspositively coupledfto said anode for supplying the frequency to bedivided thereto, said i frequency divider being so constructed vandarranged that there is an absence of anode cur:- rent iiow therein inthe absence of applied 'waves from said means, said applied waves havingsuch magnitude as to cause said tube to draw current at certainpredetermined intervals, to thereby produce a voltage pulse wheneversaid tube draws current and which travels along said line from the anodeend to the grid end, said lter line having such constants that itproduces a delay in the voltage pulse traveling along its length whichis equal to a predetermined integral number of cycles of the appliedwave.

11. A frequency divider comprising a vacuum tube having an anode, acathode and a pair of control electrodes, a section of transmission lineconnected at one end to said anode andatits other end to one of saidcontrol electrodes, means coupled to said anode for supplying theretowaves of the frequency to be divided, said waves having positive andnegative peaks, said frequency divider being so constructed and arrangedthat there is an absence of current now therein in the absence of saidwaves being supplied to said anode, said applied waves having suchmagnitude as to cause said tube vto draw current at predeterminedintervals to thereby produce a voltage pulse whenever said tube drawscurrent and which travels along said line from the anode end to the gridend, said line having such constants that it produces a delay in thevoltage pulse traveling along its length which is equal to an integralnumber, including unity, of cycles of the applied wave, and means forsupplying keying pulses to the other grid of said tube, the repetitionrate of said keying pulses being synf chronously related to the waveswhose frequency is to be divided and so phased that the starting edge ofthe keying wave occurs during the time interval that said anode isnegative relative to the cathode.

` STUART WILLIAM SEELEY` REFERENCES CITED i The .,following referencesare of record in the file of this patent:

UNITED STATES PATENTS Date"

